Numerous medical procedures are performed today that involve the purposeful destruction of selected nervous tissue for therapeutic effect. Such procedures may be performed on nerves that are causing pain or other undesired physiological effects such as abnormal autonomic activity. For purposes of pain management, for example, nerve ablation procedures are commonly performed on peripheral, spinal, or pelvic nerves.
A specific example of a physiological consequence of abnormal autonomic activity is hypertension. The sympathetic nervous system plays an important role in circulatory and metabolic control and is a major contributor to the development of hypertension. One pathway by which elevated sympathetic nerve activity initiates and sustains the elevation of blood pressure is via the kidneys. Increased sympathetic outflow to the kidneys via sympathetic efferent nerves leads to both acute and long-term blood pressure elevations due to increased sodium and water retention, increased renin release, and alterations of renal blood flow-effects. Signals from renal afferent sympathetic nerves are also believed to contribute to hypertension by acting on the brain to increase sympathetic drive. Adequate renal function is not dependent on these nerves, as evidenced by patients who undergo transplantation with denervated kidneys and survive without complications. Catheter-based renal sympathetic nerve ablation has been shown to be a viable therapeutic approach for the treatment of hypertension in certain patients. In this procedure, an intravascular catheter with an ablating instrument is introduced into the renal artery. The renal plexus is a network of nerve fibers located around the renal artery, primarily in the adventitia, and contains postganglionic fibers from the sympathetic nervous system as well as sympathetic afferents. The nerve fibers from the plexus enter the kidney with the branches of the renal artery. Applying RF (radio-frequency) energy from the ablating instrument to these nerves effectively denervates the kidney to prevent the sympathetic mechanisms described above from contributing to a patient's hypertension.